You could try Firefox with File / Work Offline (I'm not sure of the equivalent for other browsers).

uBlock rule:

    ||icanhazip.com^$xmlhttprequest,domain=thedisconnect.co

> turning off wifi does nothing.

I tried turning off my wireless interface but that didn't accomplish the desired result because my computer uses Ethernet to connect to the network.

(Yes, I know, "wifi" is now a synonym for "any external network connection" but I also have the--possibly irrational--view that people who claim to understand "the Internet" should also know to make the distinction.)